Signal controlled keying circuit



Dw 15, 1942- c. N. GILLESPIE, JR 2,304,998

SIGNAL CONTROLLED'KEYING CIRCUIT Filed March 29, 1941 INVENTOR Ckarles/il Gillespie J1:

ATTORNEY Patented Dec. 15, 1942 SIGNAL CONTROLLED KEYING CIRCUIT Charles N. Gillespie, in, Brooklyn, N. m, assignmto Radio Corporation of America, a corporation of Delaware Application March 29, 1941, Serial No. 385,809

9 Claims.

This invention relates to the remote control of electrically operated devices, such as relays, by means of a signal of radio or audio frequency. More specifically, it relates to a high speed keyer circuitwhere a direct current relay or other response device must be used.

It is an object o! my invention to provide 9.

means for utilizing a single frequency for sig- In carrying out my invention I have found that a signal of proper frequency may be employed to produce a high voltage in a series resonant circuit associated with a gas discharge tube of the triode type. This high voltage is preferably applied negatively to the cathode of such a tube in order to ignite the same. The resulting discharge is used to pass current in an anode circuit which may include a relay of any suitable type. Connected to the output cir cult of the gas triode I also employ an auxiliary discharge tube which may be of the vacuum type, if desired, for momentarily reducing the anode voltage of the gas triode to a point below its extinction potential. The control electrode of the auxiliary tube, and the cathode of the gaseous discharge tube, are both subject to control by the signal.

In circuits heretofore known an alternatin voltage of commercial frequency is customarily used on the plate of the gas tricde. Such practice eliminates the need for auxiliary extinguishing devices, but results in a circuit useful only for low speed signaling.

My invention will now be described in more detail, reference being made to' the accompanyin: drawing the sole figure of which shows a preferred circuit arrangement.

Thecircuit arrangement as shown includes input terminals I and ,2 for impressing thereon I A source of direct current operating potential it is connected through resistor ii and relay 1 to the anode A in tube 5. The negative side oi! the source it is directly connected to the input I terminal 2, and through inductance ii (and shunt resistor 8) to the cathode K. A fixed bias potential for the control grid G is derived from a suitable connection thereof to the voltage divider I3, it. This bias potential is somewhat positive with respect to'the cathode, but is safely below the ignition point.

The auxiliary tube it, which is used for extinguishing the tube 4, is preferably of the tetrode type. Its cathode is connected to the negative terminal oi source [5. Its anode is connected to the junction between relay 1 and resistor ii. Its screen grid is connected to the positive terminal of the source it and its control grid is connected to a grid leak resistor 9 and shunt condenser 8 which are connected to the adjustable tap on the voltage divider 5.

When a signal of the resonant frequency of inductance 5 and capacitance 3 is impressed on terminals i and 2, the signal voltage appearing across inductance 5 will be high. Negative peaks of this voltage are applied to the cathode K of the gas triode 4. The resulting increase of potential diiierence between the cathode K and control grid G (carried at a fixed bias) causes the tube l to ignite and to conduct a current.

The resulting plate current will operate the relay i. Signals of frequencies other than the resonant frequency of inductance 5 and capacitance 3 will have a negligible eflfect on the circuit, since the voltage across inductance 5 will be small for all frequencies except the resonant frequency.

The high voltage appearing across inductance 5 when a signal of the resonant frequency is applied to the circuit, is also applied to the grid of the vacuum tube iii, which acts as a grid leak detector. This will cause the average plate current of this tube to decrease to a value whichwill cause a very small voltage drop across the resistor ii. The total drop across resistor Ii due to the plate current of tube ill and tube I will not be so large as to cause the plate voltage of tube 4 to fall to the extinction potential. Therefore, the conduction of tube 4, which was started vent the plate current of tube a from lowerins its plate voltage to the extinction point.

Upon removal of the signaling frequency, vacuum tube is will draw full plate current, since a substantially zero bias is then applied to its grid through the grid leak resistor 9. This increased plate current will cause an increase in'voltage drop across resistor ll, whose value is chosen so that this drop will lower the potential on theplate of tube 4v below the extinction point. This will cause tube 4 to cease conducting current and the relay 1 will become de-energized.

The value of potentiometer 6 should be madeas high as possibleso that the "Q" of the inductance will not be seriously lowered.

This circuit arrangement has been found to be very'dependable in responding to relatively weak signals of the frequency to which the resonant circuit 3, 5 is selective. Furthermore, it requires only a small variation in the signal voltage to control the tube it. The control potential as applied to the grid of tube I0 is varied between a. substantially zero bias in the absence of the signal and a cut-oil bias in the presence oi the signal.

It will be understood by those skilled in the art that my invention is capable of use in connection with other devices than the relay I and that the circuit arrangements may be varied in certain particulars without departing from the spirit of the invention.

I claim:

1. In a keying system, a gaseous discharge tube having a cathode, an anode and a control grid; means normally subjecting said control grid to a negative biasing potential with respect to said cathode, a circuit resonant to the frequency of certain keyed signals by which the moments of ignition and extinction of. said tube are to be controlled; means including a connection from a suitable point on said resonant circuit to the cathode of said tube whereby a signal voltage appearing across a reactive element of said resonant circuit causes said tube to ignite; an anode circuit for said tube including a utilization device, an impedance, a direct current source, and the inductive element of said resonant circuit; and means including an auxiliary discharge tube for causing the moments of extinction of said gaseous tube to be controlled by said signals, said auxiliary tube being powered] by said source, and having a control grid normally biased to permit current flow in the absence of signals, and subject to a cut-ofl bias in the: presence of signals. I

2. In a system according to claim 1, the combination so defined in which said utilization device is constituted as an electromagnetic relay,

3. In a system according to claim 1, the combination so defined in whichthe discharge tube of the last said means is constituted as a tetrode having its screen grid subjected to a positive potential derived from said direct current source.

4. In .a signal-controlled circuit arrangement for actuating an electromagnetic relay, 2. tube ductive and causesthe gaseous discharge in the having "a gaseous discharge path in. series with the winding of said relay; an inductance, a di-=' rect current source and an impedance also in circuit with said winding and said discharge path; a pair of signal input terminals connected through a capacitor to the terminals of said inductance, said capacitor and inductance icrmd a series resonant circuit tuned to the frequency of the applied signals; an igniter grid in said tube; voltage divider connections from said first said tube to be extinguished.

5. In a keying system, a gaseous discharge tube having a cathode, a control grid, and an anode; an output circuit for said tube, said output circuit including an inductance connected to said cathode, a direct current source, an impedance, and a utilization device connected to said anode; a pair of input terminals one of which is directly connected to the negative terminal of said source and the other of which is coupled through a capacitor to the Junction between said cathode and said inductance, said capacitor and said inductance forming a series resonant circuit tuned to a predetermined frequency of signals applied to said input terminals; a voltage divider connected in shunt with said inductance; a second voltage divider connected across the terminals of said direct current source; gas discharge extinction means constituted by a vacuum discharge tube the anode of which is connected to the junction between said impedance and said utilization device, and the cathode of which is connected to the negative terminal of said direct current source; and two control grid circuits each connected to an intermediate point on an appropriate one of said voltage dividers, the first said voltage divider being arranged to supply a variable bias to the control grid of said vacuum tube and the second said voltage divider being arranged to supply a fixed bias to the control grid of said, gaseous tube.

6. Apparatus for actuating an electromagnetic relay in response to tone-modulated marking and spacing signals, said apparatus comprising a gaseous discharge tube the discharge path of which is in circuit with the winding of said relay and is powered by a direct current source connected at the positive terminal through a resistor to the winding of said relay and thence to the anode of said tube, the cathode of said tube being in circuit with the negative terminal of said source, a tuned signal input circuit resonant to the tone frequency of said signals, said input circuit including connections tosaid cathode and to a control electrode in said tube, and discharge extinguishing means constituted by an auxiliary tube the discharge path of which is in circuit between the anode and cathode of said gaseous discharge tube, said means including in said auxiliary tube a control grid connected to an adjustable tap on a voltage divider which shunts an inductive portion of said resonant input circuit, and said means being operative in response to the presence of signals to apply a cut-ofi bias to said control grid and upon cessation of signals to render said auxiliary tube conductive, thereby to reduce the potential drop in said gaseous discharge path to the extinction point.

7. In a circuit arrangement for utilizing a gaseous discharge tube to key a current through the winding of a relay in response to the reception of tone modulated signals, where such signals may be varied as to the duration of their asoaoes marking and spacing elements, said circuit arrangement having an auxiliary tube the dis charge path of which is subject to control by said signals, the method of igniting and extinguishing said gaseous discharge tube which comprises resonating the input circuits for both said tubes at the tone frequency of said signals, causing the gaseous discharge tube to be ignited and the auxiliary tube to be blocked simultaneously upon reception of the tonal wave front of each said signal, and causing said gaseous discharge tube to be extinguished by the unblocking of said auxiliary tube at the tonal wave termination of each said signal.

8. In a keying circuit arrangement, a direct current relay to be energized upon reception of a tone modulated marking signal, a gaseous triode tube having its discharge path in series with the winding oi. said relay, an auxiliary tube having its discharge path in shunt with a portion of the circuit of said relay and gaseous tri'ode, a signal to the signaling tone irequency, and connections between said resonant elements and certain electrodes of both said tubes such that the gaseous triode is ignited at the commencement of a mar ns signal and simultaneously said auxiliary tube is blocked, and such that the unblocking of said auxiliary tube upon cessation of a marking signal causes the voltage drop in the gaseous triode to be reduced below the critical voltage necessary to sustain ignition therein.

' 9. In a keying system responsive to the reception of tone modulated signals, a series-resonant circuit connected across two input terminals of said system; a gaseous discharge tube having a cathode connected to a Junction between capacitive and inductive elements of said series-resonant circuit, and having a cathodeto-anode circuit including the inductive element of said series-resonant circuit, also a direct current source, a resistor, and a device responsive to the flow of current therethrough; an auxiliary dis- .control circuit including resonant elements tuned charge tube having its .cathode-to-anode circuit inclusive 01' said source and said vresistor; and control means for said auxiliary tuber, arranged to block the same in response to the up-building oi signal potentials across said inductive element, said control means being operable upon termination of the tonal signal wave to render said auxiliary tube conductive and thus to cause 15 extinction of said gaseous tube. 2 I

cmmms'mammrm, JR. 

